This invention relates to compositions which are polymerizable by means of free radical initiation, and more particularly, to dental adhesive and primer compositions having improved adhesion to dentin, enamel and bone.
It is most desirable, when filling a tooth cavity with a filling material, such as a polymerizable dental restorative, to ensure good adhesion between the tooth surrounding the cavity and the set (polymerized) filling material since there is thereby obtained a good seal between the set filling material and the tooth which prevents, or at least markedly inhibits, ingress of mouth fluids and bacteria into the filled cavity and thus prevents further decay or loss of the filling material. In order to achieve good adhesion between the filler material and the tooth enamel, it has been recommended to provide a primer or adhesive bonding layer intermediate the filling material and surfaces of a prepared tooth. As disclosed, for example, in Canadian Pat. No. 559,648 to Hagger, the bonding intermediate layer, which acts as an adhesive, should present polar groups toward the inorganic crystal lattice (apatite) of the tooth and be anchored by means of a non-polar group in the filling material. In order to accomplish this goal, it was taught to utilize dimethacrylglycerophosphoric acid as a polymerizable intermediate adhesive bonding layer. In practice, the surfaces in a prepared cavity of a tooth were dampened with the dimethacrylglycerophosphoric acid, usually in an alcohol medium, whereafter a paste of the filling material (monomer, polymer and room temperature effective catalyst such as sulfinic acid) was plugged into the cavity. The catalyst then caused simultaneous setting of th adhesive and filling material at the temperature in the mouth. It was also disclosed to dissolve the catalyst in the polymerizable adhesive and to spread the polymerizable adhesive solution on the surface to be bonded.
The technique disclosed in the Hagger patent was effective for bonding tooth enamel, dentin and ivory with the polymerizable filling materials existing at that time.
Another approach for aiding in the secure placement of fillings, that has been in general use for a number of years now, is the approach of first acid etching the dental preparation and then applying a low viscosity resin to penetrate the interiors caused by etching and thus prime or line the dental preparation. The primer layer is then cured, whereafter a higher viscosity polymerizable filling material is applied to the preparation. The primer usually is a lower viscosity form of the same base polymerizable filling material that will be used to fill the tooth, the difference in viscosity being primarily the result of the addition of less filler to the resin. Because the primer is basically the same system as the filling, compatibility has generally not been a severe problem.
However, as the field of polymerizable dental restorative materials has developed a need for still further improved primers and adhesives has become self-evident, particularly with respect to the need for greater bonding strength and reduction of marginal leakage between exposed dentin and enamel surfaces and the restorative filling materials.
This need led to the development of two part chemically cured adhesives, such as those described in U.S. Pat. No. 4,182,035 to Yamauchi et al and in European Patent application No. 0084407 to Bunker (corresponds to publication No. 0058483). The adhesive described in the Yamauchi et al. patent comprises a first package consisting of a free radical polymerizable monomer and a diacylperoxide, and a second package comprising an alkali or alkaline earth metal salt of an arylsulfinic acid and a volatile solvent. The adhesive disclosed in the Bunker application comprises a polymerizable phosphorous compound, a tertiary amine, a polymerization catalyst, a diluent, and an effective amount of a metal selected from iron, copper, manganese, cobalt, tin, chromium, nickel and zinc dissolved in a polar solvent. The metal dissolved in the polar solvent is stored separately from the remainder of the composition and is added thereto prior to the application of the adhesive to a tooth surface.
While self-curing multi-part systems of the type described above can provide improved adhesion between a tooth surface and a polymerizable filling material, the limitations associated with the need for storing two or more components in separate containers until immediately before use can not be minimized. For example, the need for mixing several components prior to use requires not only time, but skill, since it is essential that the proper proportions of polymerizable material, catalyst and accelerator be mixed, without the inclusion of air bubbles, which act as a polymerization inhibitor, so as to ensure the formation of a polymerized adhesive having the desired physical characteristics. Then, too, polymerizable adhesives of the above type normally have limited working times available and must be hardened for a predetermined length of time before a polymerizable filling material can be plugged over the adhesive in cavity. Following this, one must wait until the filling material and the underlying adhesive have hardened sufficiently to allow the filling material to be shaped and finished with burrs and/or abrasives and the like in order that the rigid filling material does not transmit forces which can dislodge and break or exceed the adhesive bond strength of the newly placed two component adhesive to dentin.
Finally, self-curing two part adhesive systems of the type described above, preferably are used with multi-part self-curing filler materials.
One of the recent advances in polymerizable filling systems has been the one component light curing composite filling material that can be cured in from about 5 to about 40 seconds as contrasted to the 5 to 15 minutes of cure time required for the self-curing two component system and does not require dentist office time for mixing. One component light curing filling materials are premixed in the factory to include all catalysts and activators in a single component package that is essentially free of air, needs no subsequent mixing and is sold in a light-tight package in order to exclude activating light. These light curing one component composite filling materials may be applied directly into the prepared restorative cavity and are hardened in a matter of seconds by the application of visible or ultraviolet light. This new one component product has brought about a need for new and improved primers and adhesives which are compatible with strong biologically safe adhesion to the tooth and to the new filling materials. Preferred new primers and adhesives would, in most instances, be convenient one component actinic light cure compositions.